Carlos Trejo

Diversity of unavailable polysaccharides and dietary fiber in domesticated nopalito and cactus pear fruit (Opuntia spp.).

The aim of this study was to quantify mucilages, pectins, hemicelluloses, and cellulose of nopalitos (edible, as vegetable, young cladodes of flat‐stemmed spiny cacti) of most consumed Mexican cultivars, and sweet and acid cactus pear fruits of Opuntia spp. The hypothesis is that, regardless of their unavailable polysaccharides diversity, nopalitos and cactus pear fruits are rich sources of soluble and insoluble dietary fiber. Twelve cultivars of Opuntia spp. were used. Nopalitos had a significant variation in structural polysaccharides among the cultivars: mucilages (from 3.8 to 8.6% dry matter (DM)) averaged near a half of pectins content (from 6.1 to 14.2% DM) and tightly bound hemicelluloses (from 2.2 to 4.7% DM), which were the less abundant polysaccharides, amounted 50% of the loosely bound hemicelluloses (from 4.3 to 10.7% DM). Acid fruits (or ‘xoconostle’) had significantly higher unavailable polysaccharides content than sweet fruit, and contain similar proportions than nopalitos. Unavailable polysaccharides represent a high proportion of dry tissues of nopalitos and cactus pear fruits, composition of both of these soluble and insoluble polysaccharides (total dietary fiber) widely vary among cultivars without an evident pattern. Nopalitos and cactus pear fruit can be considered an excellent source of dietary fiber.

Root growth and proline content in drought sensitive and tolerant maize (Zea mays L.) seedlings under different water potentials

The effect of substrate water potential (Ψ W ) in root growth and proline content of maize seedlings of Tuxpeno Sequia C0 (TSC0) and Tuxpeno Sequia C8 (TSC8), sensitive and resistant to drought respectively, were evaluated. Seventy two hours old seedlings, with 5 cm root length, were maintained for 24 h in vermiculite at Ψ W between −0.03 and −2.35 MPa. Root length, fresh and dry weight, number of lateral roots and proline content were evaluated. Root enlargement of TSC0 was significantly higher than TSC8 at −0.03 MPa, but the response was opposite at low substrate Ψ W . The number of lateral roots was reduced in 23% in TSC8 at the lowest substrate Ψ W (−2.35 MPa) but it was not significantly affected in TSC0. A higher proline content was quantified in the cell division root region than in differentiation root region in both maize populations (5.64 and 6.96 μmol 100 mg −1 of dry weight in TSC0 and TSC8, respectively); and Ψ W between −0.65 and −2.35 MPa induced a drastic and significant increase of prolin...

Root anatomy of drought sensitive and tolerant maize ( Zea mays L.) seedlings under different water potentials

The effect of substrate water potential (ψW) in anatomical characteristics of root seedlings of maize Tuxpeno Sequia C0 (TSC0), drought sensitive, and Tuxpefto Sequia C8 (TSC8), drought resistant, were evaluated. Seventy two hours old seedlings, having an average root length of 5 cm, were maintained for 24 h in vermiculite at ψW of −0.03, −0.65, −1.48 and −2.35 MPa. Anatomical characteristics from both differentiation and cell division root regions were evaluated. Lowest ψW diminished significantly (P=0.0020) transverse root area, number of cells in the cortex parenchyma, thickness of epidermis, exodenmis and cortex, and number of metaxylem vessels in both maize populations. Number of metaxylem vessels and cortex thickness was affected only in TSC0 (15% in both cases); in contrast, the number of cortex cells in the differentiation root region increased 25%, independently of the ψW, and the thickness of the xylem wall from the differentiation root region increased 93% at ψW of −2.35 MPa, in both maize populations. Results suggest that the recurrent selection for drought tolerance induced a significant thinning of the protoderm (78%), endodermis (17%), and xylem vessels (14%) in Tuxpefto maize root and modified the response of root to substrate ψW, including several anatomical changes.

Seed germination of Agave species as influenced by substrate water potential.

BackgroundPlants of Agave spp. perform Crassulacean acid metabolism (CAM) and are highly drought-tolerant, but little is known concerning seed germination under low water availability. The aim of this study was to assess the effect of substrate water potential (ΨW) on seed germination and contrast hydrotime parameters of seven valuable and commercially-important Agave species from different geographical distributions and climatic regions of Mexico. Our hypothesis was that seed germination of Agave species is not affected by low water availability independently of seed biomass and the climate of their distribution area.ResultsSeed germination (at 25°C and in the dark) between 85 and 100% for all species occurred within 80–180 h at -0.03 MPa and 250–430 h at -1.0 MPa. Seed germination at -1.5 MPa declined to less than 50% (p < 0.05) for A. asperrima and A. cupreata but did not change significantly for A. americana var. marginata, A. lechuguilla and A. striata, although they showed the lowest mean base water potential (-2.01 to -2.64 MPa). Seed germination of 40% Agave species, from arid and semi-arid climates in this study, was not affected by the lower ΨW.ConclusionGermination of seeds of Agave species is moderately affected by low water availability, is partially dependent of their ecological distribution, and is independent of seed mass.

Differences in seed germination of wild and domesticated common bean (Phaseolus vulgaris L.) in response to storage

This study compared the effect of storage on the germination of wild and domesticated common bean (Phaseolus vulgaris L.). Two sizes (large and small) of intact and mechanically scarified seeds of wild common bean from Salti to, Durango and La Malinche, Tlaxcala, Mexico, and the cultivars Bayo Mecentral and Amarillo were stored at 300 and 75% RH for 0, 30, 60 and 90 days. Germination in the dark at 25C was evaluated. In general, mechanical scarification at zero days of storage induced a reduction in the time to the start of germination (5 to 83h) and in the time to complete germination (126 to 341h) of wild seeds, but it did not affect the percentage of germination. After 30d of storage the germination of small intact wild seeds from Tlaxcala and cv. Bayo Mecentral was reduced to 30%; but after 60d of storage, wild small seeds from Tlaxcala and both cultivars were almost 100% inhibited. In contrast, as an average, intact and scarified wild seeds from Durango and larger seeds from Tlaxcala reached 52 and 25% of germination respectively. Although 90d of storage affected drastically both wild and domesticated beans, even after this long storage, 3 to 15% of wild seeds germinated. The results are consistent with the speculation that an increased sensitivity of common bean seeds to storage under high temperature and elevated RH could be a concomitant result of selection for some other traits such as targe seed during domestication.